Yes, a real drag. I was hoping that would be the last of the problems with that switch deck. I put a lot of work into it but looking positive I know how those delicate assemblies work...err...don't work.

Thanks for keeping watch for a 465B.

I dunno who I pissed off at USPS. They told me you would have that package by last Tuesday. Obviously that didn't happen.

Yes, a real drag. I was hoping that would be the last of the problems with that switch deck. I put a lot of work into it but looking positive I know how those delicate assemblies work...err...don't work.

Thanks for keeping watch for a 465B.

I dunno who I pissed off at USPS. They told me you would have that package by last Tuesday. Obviously that didn't happen.

A long time ago, I got a temp gig, delivering mail. Based on my brief experience, it is easy for me to imagine a package getting lodged underneath the seat of a delivery van, only to be found when the seat jams while being adjusted.

Usually you put down what you want to pay for it and cross your fingers, toes and large intestine that they accept it

Edit: well just checked out the TF2015 against my power meter and on a scope. The attenuator does indeed appear to be bust. But not badly. I've taken expected vs actual measurements for all positions and am going to sit with the SMM and work out what the failure is likely to be. Then it's plumbing time!

Usually you put down what you want to pay for it and cross your fingers, toes and large intestine that they accept it

Edit: well just checked out the TF2015 against my power meter and on a scope. The attenuator does indeed appear to be bust. But not badly. I've taken expected vs actual measurements for all positions and am going to sit with the SMM and work out what the failure is likely to be. Then it's plumbing time!

We apparently are all victims of Gorillas who enjoy destroying attenuators.

With things like those it doesn't even matter what it is, what it is supposed to do and whether it still does it. Something made like that is just a pleasure.

Very true indeed.

Well I found the problem. As expected. Reverse power overload with attenuators switched in. Quick trick with a 50 ohm attenuator strip. If you switch out all the attenuators so it's 0dBm attenuation, then measure the resistance at the junction point at each node on the pi attenuator network it should be around 50 ohms. If it isn't, smoke has come out somewhere. Smoke most likely came from somewhere closest to the output.

Soooo, this is a 96.3 ohm parallel pair and 71.2 ohm series. Time to go shopping for some suitable thin film resistors that have to be good up to 520MHz...

Quick shot of the whole assembly opened. Note the yellow things - they are transmission line stubs / gimmicks by the looks.

Edit: can I get a 96.3 ohm resistor? Can I hell!

Edit 2: went through a massive box of resistors I have and found a used 97.6 ohm 1/4W MF one! Close enough. Have checked all the others and bunged that in and reassembled it and it works down to -60dBm. I can't measure any lower than that at the moment and I'm not sure if I care about miniscule powers like that for now. My power meter is reporting flat response to 405MHz as well which I was happy with. There's a 0.4dB error on the 10dB attenuator (4%) but I can live with that. And on that note, as it's 01:25 in the morning here, bed!

Edit 3: before I disappear, the enclosures for the attenuators are aluminium and one leg of the resistor is soldered to it. Rather than try and get a good joint on fresh alu which is a dick, I soldered it to the existing solder, adding some 62/36/2 silver bearing. This did the trick.

Apart from the random minor layer shift late in the print the two black bits are done and feel comfortable even in my large paws and the oval shape seems to work. Time to load up the safety Red for the rest.

Thinking a separate thread in Projects is in order BTW rather then hiding it here as I wouldn't mind trying to get a 2-3kV Scope higher frequency version up and going too and some trial and error and some input from others will be needed.

I decided to do a little benchmark of different EMI line filters I have laying around, just to compare.

The setup was pretty simple, analysing differential mode (line to line), sweeping from 1Khz to 1Mhz. The idea was to observe the effectiveness of the low pass filter.

1- Canny Well CW1D-10A (cheap emi filter from china)

2- Delta 06GEEG3E

3- Schaffner FN372-2-31

4- Keithley 610CR line filter

I was surprised. Was expecting to change the Keithley filter but it seem to be working pretty well. I guess they knew what they were doing back then. I'm probably not going to touch it, will just make things worst

With things like those it doesn't even matter what it is, what it is supposed to do and whether it still does it. Something made like that is just a pleasure.

Very true indeed.

Well I found the problem. As expected. Reverse power overload with attenuators switched in. Quick trick with a 50 ohm attenuator strip. If you switch out all the attenuators so it's 0dBm attenuation, then measure the resistance at the junction point at each node on the pi attenuator network it should be around 50 ohms. If it isn't, smoke has come out somewhere. Smoke most likely came from somewhere closest to the output.

Soooo, this is a 96.3 ohm parallel pair and 71.2 ohm series. Time to go shopping for some suitable thin film resistors that have to be good up to 520MHz...

Quick shot of the whole assembly opened. Note the yellow things - they are transmission line stubs / gimmicks by the looks.

Edit: can I get a 96.3 ohm resistor? Can I hell!

Edit 2: went through a massive box of resistors I have and found a used 97.6 ohm 1/4W MF one! Close enough. Have checked all the others and bunged that in and reassembled it and it works down to -60dBm. I can't measure any lower than that at the moment and I'm not sure if I care about miniscule powers like that for now. My power meter is reporting flat response to 405MHz as well which I was happy with. There's a 0.4dB error on the 10dB attenuator (4%) but I can live with that. And on that note, as it's 01:25 in the morning here, bed!

Edit 3: before I disappear, the enclosures for the attenuators are aluminium and one leg of the resistor is soldered to it. Rather than try and get a good joint on fresh alu which is a dick, I soldered it to the existing solder, adding some 62/36/2 silver bearing. This did the trick.

Good work, I'm not surprised about the 96.3 ohm value, as I mentioned they are built to a very demanding spec. Where they used, they have to perform well, each and every time and between the various sections, Marconi, Marconi Radar, Marconi Marine and English Electric Valve, they had sufficient clout to force manufacturers to limited production runs. These runs would be of values like your 96.3 ohms with a tight tolerance band. Their motto was perfection, not 2nd best.

@bd139: It is a bit curious that you cannot get this resistor. The value seems to have been used frequently, as I found in my stock 963 Ohms and 9.63kOhms, both with 0.1%. Sadly, not the 96.3 Ohms.Correction: the first are 953 Ohms.

I decided to do a little benchmark of different EMI line filters I have laying around, just to compare.

The setup was pretty simple, analysing differential mode (line to line), sweeping from 1Khz to 1Mhz. The idea was to observe the effectiveness of the low pass filter.

I was surprised. Was expecting to change the Keithley filter but it seem to be working pretty well. I guess they knew what they were doing back then. I'm probably not going to touch it, will just make things worst

am curious about what you used to make those phase/gain plots.

have an aim 4170 but it is only a one port unit good for S11 (and it maybe it is recommended only for use above 100Khz?)

have been thinking about picking up a digilent analog discovery for S21 but have never had one in hand to see how it performs.

@bd139: It is a bit curious that you cannot get this resistor. The value seems to have been used frequently, as I found in my stock 963 Ohms and 9.63kOhms, both with 0.1%. Sadly, not the 96.3 Ohms.Correction: the first are 953 Ohms.

Yes I thought that was a bit weird but it turns out it's not a standard E-series value apparently. Basically the reason it exists is if you design a 10dB attenuator for a 50 ohm system the ideal value is 96.25 ohms for this resistor, rounded to 96.3 on 1DP. This gives a stupidly good return loss for the attenuator (-120dB in theory). Looks like you can get RN60C in that size but they are out of stock everywhere with weeks lead times and stupid min orders. Boo hiss

On amateur radio stuff, it's not *that* important to get it exactly right usually so the pi network is rounded to 100 ohms parallel and 68 ohms series for 10dB which is close enough. RL is not as good at around -50dB and the attenuator isn't that accurate but it'll do.